iBALT

iBALT stands for inducible bronchus-associated lymphoid tissue. It is a type of tertiary lymphoid organ that can form in the lungs in response to inflammation or infection. Unlike constitutive bronchus-associated lymphoid tissue, iBALT arises de novo in adult lungs and is not present in every healthy individual.

Histologically, iBALT comprises organized lymphoid structures with B cell follicles, often containing germinal centers, surrounded by T cell zones. It may also include dendritic cells and specialized venules (high endothelial venules) that support lymphocyte trafficking. The local architecture resembles secondary lymphoid tissues and reflects ongoing antigen-driven immune responses.

Development of iBALT is driven by local immune signals and chemokines that recruit and organize lymphocytes, such as CXCL13, CCL19, and CCL21, along with lymphotoxin pathways and inflammatory cytokines. Its formation is influenced by persistent antigen exposure and inflammatory conditions, including viral or bacterial infections and chronic inflammatory states.

Functionally, iBALT can support local antigen presentation and adaptive immune responses within the lung. It can facilitate local antibody production, including IgA, and generate memory B and T cells at the site of inflammation. In this way, iBALT may contribute to pathogen clearance but can also sustain chronic inflammation under certain conditions.

Clinical significance and research on iBALT remain context-dependent. It has been observed in various human lung conditions—such as after infections or in chronic inflammatory diseases—and in animal models. Its presence may be associated with differing outcomes, and researchers are exploring its implications for mucosal immunity, vaccination strategies, and therapies targeting tertiary lymphoid structures.